Cross Island Line


Purpose and Benefit of Cross Island Line (CRL)

Spanning fully underground across Singapore, the Cross Island Line (CRL) will be about 50-60 km in length. When fully completed, it will serve existing and future developments in the eastern, western, and north-eastern corridors, linking major hubs such as the Jurong Lake District, Punggol Digital District and Changi region.

The CRL will be a key part of our MRT network, providing a faster commute between the east and the west.  It will connect all existing radial MRT lines with close to half of the CRL stations being interchange stations. Besides relieving the load on several of the existing MRT lines, the CRL will provide commuters with many more travel routes to their destinations, encouraging more people to switch from private to public transport.  The projected daily ridership of the entire CRL is more than 600,000 in the initial years, increasing to over 1 million in the longer term.

CRL will be constructed in phases.  LTA has since announced the alignment and stations for the first phase of CRL from Changi to Bright Hill. Works on the first phase will begin in 2020 and complete around 2029.

map of the cross island line

Underground Alignment Options for CRL

As the Central Catchment Nature Reserve (CCNR) is environmentally rich with diverse native flora and fauna, LTA is considering two underground alignment options for a subsequent phase of the CRL in the vicinity.  The first (direct alignment) option would pass deep beneath the CCNR while the second (skirting alignment) option would go underground around the CCNR (see Figure 1).

Figure 1: Two Underground Alignment Options for CRL in the Vicinity of the CCNR

The key facts about the two alignment options are as follows: 

i) Direct alignment option

  • 4km tunnel in total, with 2km deep under the CCNR and the remainder outside the CCNR
  • No physical structures on the surface level within the CCNR
  • Travelling time: approximately 5 minutes (from Bright Hill to the next station)

ii) Skirting alignment option

  • Tunnels skirting around (and away from) the CCNR
  • A 9km tunnel route length under roads as well as residential and commercial buildings
  • Travelling time: approximately 11 minutes (from Bright Hill to the same next station)

Where Are We Now?

To allow an informed decision on the final alignment for the CRL, LTA commissioned in 2014 an Environmental Impact Assessment (EIA) for both alignment options.  The LTA adopted a robust two-phase EIA process for the two alignment options.

Phase 1 evaluated the existing ecosystem and physical conditions of the CCNR as well as the environmental impact of site investigation (SI) works within the CCNR.  Phase 1 had been completed with the report gazetted and published on the LTA website in 2016.  The findings of the SI works (carried out following the report) were used to inform Phase 2 of the EIA.

Phase 2 assesses the potential environmental impact of the construction and operations of the CRL as well as the required mitigation measures.  LTA sought inputs from, and engaged with, the relevant stakeholders as part of this process.  This phase of the EIA has recently been completed.    

Gazette of the EIA (Phase 2) Report

With the completion of the Phase 2 EIA, LTA gazetted the EIA Report on 2 September 2019.  The gazetting is to allow public viewing and feedback on the findings of the Report.  The Report does not recommend a preferred alignment option.  

No decision on the alignment option has been made.  The decision on the final alignment will be based on factors such as connectivity, travel times, costs as well as impact on home owners and the environment.

LTA have devised robust engineering schemes for the two alignments.  These schemes define the geographical focus and construction techniques to be adopted that informed the EIA.  The engineering schemes are robust and independently reviewed by LTA’s International Panel of Advisors (IPA)[1].  The IPA comprises internationally renowned experts in geotechnical and tunnel engineering, who concluded that with control measures in place, tunnelling along either alignment option is safe.

The EIA, by Environmental Resource Management (S) Pte Ltd (ERM), was rigorously undertaken based on an internationally-recognised framework and relevant authoritative references.  ERM is a global specialist in environmental, social, health, safety and risk management consulting services that have done similar EIA works in the UK, China and Hong Kong.  The EIA Report, too, was independently reviewed by an appointed consultant.  (Figure 2 provides an overview of the approach for the Phase 2 EIA prior to the Gazette).

Figure 2: Overview of Approach for Phase 2 EIA 

Engineering Schemes in a Nutshell

Both the direct and skirting alignment options will be fully underground.  LTA have designed a set of engineering schemes to ensure safe tunnelling and that all surface works will be carried out outside the CCNR and away from existing buildings.  (See Figure 3 for the detailed underground alignments as well as all the surface worksites, marked as coloured boxes, all of which are outside the CCNR).  For both underground alignment options, the tunnel boring machines deployed will be based on state-of-the-art technology customised to local site conditions and configured with advance control and monitoring systems.

Figure 3: Details of the Direct (Blue) and Skirting (Pink) Alignment Options and Surface Worksites Outside CCNR

The tunnel for the direct alignment option will be around 70m below average ground level beneath the CCNR so that tunnelling will be carried out fully in hard granite rock.  (The 70m depth is roughly equivalent in height to a 25-storey HDB block; this is as illustrated in Figure 4.  See also Figure 5 which provides a cross-sectional perspective of CRL operations underneath the CCNR.)  Tunnelling at 70m underneath the CCNR and fully in hard granite rock will provide added assurance from the engineering and stakeholder perspectives.  

Figure 4: Depth of Tunnelling Works in Hard Granite and Equivalent in Height to a 25-storey HDB Block

Figure 5: Perspective of Underground Train Operations Beneath CCNR for Direct Alignment Option

As for the skirting alignment option, the tunnels will be constructed in built-up areas and at depths of about 45m below average ground level.  This is to ensure that the tunnelling will be safe for buildings and away from existing underground infrastructure along this alignment.  Such underground infrastructure includes MRT and cable tunnels. (See Figure 6 on the details of the tunnelling plan to minimise impact on existing buildings and underground infrastructure).

Figure 6: Proposed Tunnels for the Skirting Alignment Option to Minimise Impact on Buildings and Underground Infrastructure

The EIA in a Nutshell

To ensure the robustness of the EIA, LTA appointed ERM, a leading global provider of environmental, social, health and risk management consulting services, to undertake the studies and assessment.  With over 35 years of experience conducting impact assessments and more than 140 offices in 44 countries worldwide, ERM has undertaken multiple projects on environmental and biodiversity studies or surveys in Singapore as well as in other jurisdictions such as the UK, China and Hong Kong.

ERM carried out the EIA in accordance with an internationally recognised process and referenced with international standards[2] where relevant guidelines are not available in the Singapore context.  Figure 7 outlines the scope and methodology of EIA’s approach to the EIA which covers the construction and operation of the CRL for both the direct and skirting alignment options as well as the mitigation measures for the impacts assessed.   

Figure 7: EIA Scope and Methodology

The EIA assessed the impacts during the construction and operation of the CRL of the relevant environmental factors (of noise, air quality and ecology for instance) on the flora, fauna and the human communities for the two alignment options.  These impact assessments were based on the engineering schemes developed.  They are largely confined to the worksites outside the CCNR (for the direct alignment) and away from residential areas (for the skirting alignment) as well as the tunnel alignments deep underneath the CCNR (for the direct alignment) or around the CCNR (for the skirting alignment).

Based on the EIA, both underground alignments are feasible.  This is as the residual impacts for the factors studied are largely moderate or below.  Moderate impact indicates small effects that are around existing conditions and/or within accepted standards.

To ensure that the EIA findings and impact assessments are robust, LTA engaged an independent reviewer[3] to verify the report and had incorporated relevant stakeholder inputs during the EIA Report review process.


We are pleased to share with you in the link below the detailed Phase 2 EIA Report. 

For further enquiries and feedback related to the Gazette, please email

[1] The members to the IPA are appointed on a two-yearly basis by LTA. For the 2017-2019 term, the IPA was chaired by Prof Yong Kwet Yew (Singapore), NUS Senior Vice President and Professor of Civil Engineering, whilst the other IPA members included Mr John Busbridge from Canada, Ex-President Golder Associates on Global Operations; Mr Eddie Woods from the United Kingdom, Tunnel Discipline Lead for UK High Speed 2 and ex-Chief Engineer Thames Tideway Tunnel; Prof Lee In-Mo from Korea University, Director of Institute of Underground Space Technology and ex-President of International Tunnelling Association; Mr Tadashi Hashimoto from the Director of Geo-Research Institute in Japan and Overseas Expert of Science and Technology committee to Shanghai Municipal Commission.

[2] The biodiversity assessment for the CRL Phase 2 EIA Report took into account the international standards set out in the International Finance Corporation (IFC) Performance Standard/Biodiversity Offsets and accompanying materials.

[3] Mr. Tony O'Dempsey has been engaged by LTA as the independent reviewer for the EIA (Phase 2) Report. He was also the independent environmental consultant in Phase 1 site investigation works inside the CCNR. Tony has been working as a volunteer on various conservation projects relating to the Nature Reserves for the past 20 years and is very familiar with the forest habitats of the CCNR. An active member in the Nature Society of Singapore (NSS), he has held various positions in the past, including council member of NSS and chair of its vertebrate study group. He is a professional who has been working in the Geographic Information System (GIS) industry in Singapore for 25 years and has applied his GIS and cartography skills to the various conservation projects he has worked on.  He has a Bachelor Applied Science (Surveying) from Queensland University of Technology.